Welcome to the forum.
My manual doesn't even have 0546 code in it. My car (2009 D40 STX) doesn't have an EGT sensor. It has a pressure sensor before and after the DPF, but no temperature monitoring.
That means that either:
1) Your car has a factory-supplied EGT sensor specifically included in your vehicle because of your country's emission control regulations, or
2) Your ECU has erroneously issued this error code, which is usually the result of a difficult start (ro a completely flat battery) or a poor connection between battery and its cables, or ECU and its earth, or battery negative cable and engine block.
Checking the last one is obviously easier, quicker and cheaper.
If it's the first one, you may have to take it to a dealer, who will have your country-specific instructions on the fault. Unfortunately they WILL fix it BUT they will do it in order of the steps in their manual, so it could get expensive, but talking to the mechanic there (or seeing if you can swipe a copy of their manual, which comes on a DVD as a series of interlinked PDF files) would help.